U.S. patent number 6,407,719 [Application Number 09/786,726] was granted by the patent office on 2002-06-18 for array antenna.
This patent grant is currently assigned to ATR Adaptive Communications Research Laboratories. Invention is credited to Koichi Gyoda, Takashi Ohira.
United States Patent |
6,407,719 |
Ohira , et al. |
June 18, 2002 |
Array antenna
Abstract
An array antenna apparatus includes a radiating element (6) for
transmitting and receiving radio signals, and at least one
parasitic element (7) arranged at a predetermined distance (d) away
from the radiating element (6) and incapable of transmitting or
receiving radio signals. The parasitic element (7) is connected
with a variable-reactance element (23). A controller (100) changes
the directivity of the array antenna by changing the reactance
X.sub.n of the variable-reactance element (23). The
variable-reactance element (23) is a varactor diode (D, D1), for
example, and the controller (100) changes the backward bias voltage
Vb applied to the variable-reactance diode (D, D1) to change the
capacitance of the varactor diode (D, D1), thus changing the
directivity of the array antenna. The array antenna has a low-cost
and simplified structure compared with the prior art, while
facilitating directivity control.
Inventors: |
Ohira; Takashi (Yokohama,
JP), Gyoda; Koichi (Kyoto, JP) |
Assignee: |
ATR Adaptive Communications
Research Laboratories (Kyoto, JP)
|
Family
ID: |
16325358 |
Appl.
No.: |
09/786,726 |
Filed: |
March 8, 2001 |
PCT
Filed: |
July 06, 2000 |
PCT No.: |
PCT/JP00/04489 |
371(c)(1),(2),(4) Date: |
March 08, 2001 |
PCT
Pub. No.: |
WO01/05024 |
PCT
Pub. Date: |
January 18, 2001 |
Foreign Application Priority Data
|
|
|
|
|
Jul 8, 1999 [JP] |
|
|
11-194487 |
|
Current U.S.
Class: |
343/893; 343/750;
343/817 |
Current CPC
Class: |
H01Q
3/44 (20130101); H01Q 9/30 (20130101); H01Q
9/32 (20130101); H01Q 19/32 (20130101); H01Q
21/061 (20130101); H01Q 21/20 (20130101) |
Current International
Class: |
H01Q
21/20 (20060101); H01Q 9/30 (20060101); H01Q
9/32 (20060101); H01Q 3/44 (20060101); H01Q
19/32 (20060101); H01Q 9/04 (20060101); H01Q
21/06 (20060101); H01Q 19/00 (20060101); H01Q
3/00 (20060101); H01Q 021/00 () |
Field of
Search: |
;343/815,817,745,749,750,833,834,836,837 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
|
|
4932239 |
|
Aug 1974 |
|
JP |
|
5991707 |
|
May 1984 |
|
JP |
|
6125304 |
|
Feb 1986 |
|
JP |
|
5206717 |
|
Aug 1993 |
|
JP |
|
10154911 |
|
Jun 1998 |
|
JP |
|
Primary Examiner: Ho; Tan
Claims
What is claimed is:
1. An array antenna apparatus comprising:
a radiating element for transmitting and receiving a radio signal
therethrough;
a plurality of parasitic elements each capable of transmitting and
receiving any radio signal, said parasitic elements being arranged
at a predetermined distance from said radiating element and on a
circumference of a predetermined circle around said radiating
element;
a plurality of variable-reactance elements connected to said
parasitic elements, respectively; and
controlling means for changing directivity of said array antenna
apparatus by changing a reactance of each of said
variable-reactance elements.
2. The array antenna apparatus as claimed in claim 1,
wherein each of said variable-reactance elements is a varactor
diode, and
wherein said controlling means changes a capacitance of each of
said varactor diodes by changing a backward bias voltage applied to
each of said varactor diodes, thereby changing the directivity of
said array antenna apparatus.
Description
TECHNICAL FIELD
The present invention relates to an array antenna apparatus which
comprises a plurality of antenna elements and is capable of
changing the directivity thereof.
BACKGROUND ART
FIG. 12 is a block diagram showing a configuration of a phased
array antenna apparatus of the prior art. Referring to FIG. 12, for
example, radio signals received by a plurality of n antenna
elements 1-1 to 1-N aligned in a linear array 100 are inputted to a
combiner 4 through low-noise amplifiers (LNAs) 2-1 to 2-N and
variable phase shifters 3-1 to 3-N, respectively. The combiner 4
combines the N phase-shifted radio signals inputted to the combiner
4, and outputs a combined radio signal after combining the same to
a radio receiver 5. The radio receiver 5 subjects the combined
radio signal to processing such as frequency conversion into lower
frequencies (down conversion) and data demodulation, and then,
extracts and outputs a data signal.
The phased array antenna apparatus is an advanced antenna for
obtaining a desired radiation pattern by exciting a plurality of
radiating elements in a predetermined relative relationship among
the phases thereof. As shown in FIG. 12, a plurality of variable
phase shifters 3-1 to 3-N is used as means for setting a desired
relative relationship among the exciting phases thereof.
As shown in FIG. 12, in the phased array antenna apparatus of the
prior art, for example, a receiver side has to comprise a plurality
of low-noise amplifiers 2-1 to 2-N, a plurality of variable phase
shifters 3-1 to 3-N and the combiner 4, and thus, the apparatus is
complicated in configuration, and therefore, the cost of
manufacturing the apparatus becomes greatly higher. Then this
drawback becomes more serious, in particular, when the number of
antenna elements 1-1 to 1-N becomes larger.
It is an essential object of the present invention to provide an
array antenna apparatus, having a simple configuration as compared
to that of the prior art, and capable of remarkably reducing the
manufacturing cost thereof, and also facilitating controlling the
directivity thereof.
DISCLOSURE OF THE INVENTION
According to one aspect of the present invention, there is provided
an array antenna apparatus comprising:
a radiating element for transmitting and receiving a radio signal
therethrough;
at least one parasitic element incapable of transmitting and
receiving any radio signal, said parasitic element arranged at a
predetermined distance from the radiating element;
a variable-reactance element connected to the parasitic element;
and
controlling means for changing directivity of the array antenna
apparatus by changing a reactance of the variable-reactance
element.
Also, in the above-mentioned array antenna, the variable-reactance
element is preferably a varactor diode, and the controlling means
changes capacitance of the varactor diode by changing a backward
bias voltage applied to the varactor diode, thereby changing the
directivity of the array antenna apparatus.
Further, the above-mentioned array antenna preferably further
comprises:
a plurality of the parasitic elements, arranged on a circumference
of a predetermined circle around the radiating element.
Therefore, according to the present invention, the array antenna
apparatus according to the present invention has a very simple
structure as compared to that of the array antenna apparatus of the
prior art shown in FIG. 12, and, for example, the use of the
variable-reactance element such as a varactor diode makes it
possible to realize the array antenna apparatus capable of
electronically controlling the directivity at a direct-current
voltage. The array antenna apparatus is easily mounted to
electronic equipment such as a notebook type personal computer or a
PDA so as to serve as an antenna for a mobile communication
terminal, for example. Moreover, even when the main beam is scanned
in any direction on a horizontal plane, all parasitic
variable-reactance elements effectively function as wave directors
or reflectors and also greatly facilitate the control of the
directivity.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view showing a configuration of an array
antenna apparatus according to a first preferred embodiment of the
present invention;
FIG. 2 is a schematic diagram showing a configuration of a feeding
antenna element A0 shown in FIG. 1;
FIG. 3 is a schematic diagram showing a configuration of each of
parasitic variable-reactance elements A1 to A6 shown in FIG. 1;
FIG. 4 is a cross sectional view showing a detailed configuration
of the array antenna apparatus shown in FIG. 1;
FIG. 5 is a perspective view showing a configuration of an array
antenna apparatus according to a second preferred embodiment of the
present invention;
FIG. 6 is a perspective view showing an analytical model of the
array antenna apparatus according to the second preferred
embodiment;
FIG. 7 is a plan view showing a planar arrangement of the array
antenna apparatus shown in FIG. 6;
FIG. 8 is a graph showing a directivity on horizontal plane in a
case 1 of the array antenna apparatus shown in FIGS. 6 and 7;
FIG. 9 is a graph showing a directivity on horizontal plane in a
case 2 of the array antenna apparatus shown in FIGS. 6 and 7;
FIG. 10 is a graph showing a directivity on horizontal plane in a
case 3 of the array antenna apparatus shown in FIGS. 6 and 7;
FIG. 11 is a graph showing a directivity on horizontal plane in a
case 4 of the array antenna apparatus shown in FIGS. 6 and 7;
and
FIG. 12 is a block diagram showing a configuration of an array
antenna apparatus of the prior art.
BEST MODE FOR CARRYING OUT THE INVENTION
Preferred embodiments of the present invention will be described
below with reference to the accompanying drawings.
FIRST PREFERRED EMBODIMENT
FIG. 1 is a perspective view showing a configuration of an array
antenna apparatus according to a first preferred embodiment of the
present invention, FIG. 2 is a schematic diagram showing a
configuration of a feeding antenna element A0 shown in FIG. 1, and
FIG. 3 is a schematic diagram showing a configuration of each of
parasitic variable-reactance elements A1 to A6 shown in FIG. 1.
In the preferred embodiment, as shown in FIG. 1, the feeding
antenna element A0 and the six parasitic variable-reactance
elements A1 to A6, each of which is a monopole element, are
electrically insulated from a grounding conductor 11 made of a
conductor plate having an area large enough for lengths l.sub.o
l.sub.n (n=1, 2, . . . , 6) of the elements A0 to A6. The parasitic
variable-reactance elements A1 to A6 are spaced at a predetermined
equal distance at an angle of 60degrees on the circumference of a
circle having a radius d of, for example, .lambda./4 around the
feeding antenna element A0.
Referring to FIG. 2, the feeding antenna element A0 comprises a
cylindrical radiating element 6 having a predetermined longitudinal
length l.sub.o of, for example, .lambda./4 and electrically
insulated from the grounding conductor 11. A central conductor 21
of a coaxial cable 20 for transmitting a radio signal fed from a
radio apparatus (not shown) is connected to one end of the
radiating element 6, and an outer conductor 22 of the coaxial cable
20 is connected to the grounding conductor 11. Thus, the radio
apparatus feeds a radio signal to the feeding antenna element A0
through the coaxial cable 20, and then, the radio signal is
radiated by the feeding antenna element A0.
Referring to FIG. 3, each of the parasitic variable-reactance
elements A1 to A6 has a similar structure comprising a cylindrical
parasitic element 7 having a predetermined longitudinal length
l.sub.n (n=1, 2, . . . , 6) of, for example, .lambda./4 and
electrically insulated from the grounding conductor 11, and a
variable-reactance element 23 having a reactance X.sub.n (n=1, 2, .
. . , 6). The reactance X.sub.n of the variable-reactance element
23 is controlled by a controller 100 that is a digital computer,
for example.
One end of the parasitic element 7 is grounded in high frequency
bands to the grounding conductor 11 through the variable-reactance
element 23. For example, under such an assumption that the
longitudinal length of the radiating element 6 is substantially
equal to that of the parasitic element 7, for instance when the
variable-reactance element 23 is inductive (L characteristic), the
variable-reactance element 23 changes into an extension coil, thus
the electric lengths of the parasitic variable-reactance elements
A1 to A6 are longer than the electric length of the feeding antenna
element A0, and therefore, the parasitic variable-reactance
elements A1 to A6 operate as reflectors. On the other hand, for
instance when the variable-reactance element 23 is capacitive (C
characteristic), the variable-reactance element 23 changes into a
loading capacitor, thus the electric lengths of the parasitic
variable-reactance elements A1 to A6 are shorter than the electric
length of the feeding antenna element A0, and therefore, the
parasitic variable-reactance elements A1 to A6 operate as wave
directors.
Accordingly, the array antenna apparatus shown in FIG. 1 causes the
controller 100 to change the reactance of the variable-reactance
element 23 connected to the parasitic variable-reactance elements
A1 to A6, and thus can change a directivity on horizontal plane of
the whole array antenna apparatus.
FIG. 4 is a cross sectional view showing a detailed configuration
of the array antenna apparatus shown in FIG. 1. In the preferred
embodiment shown in FIG. 4, a varactor diode D is used as the
variable-reactance element 23.
Referring to FIG. 4, the grounding conductor 11 is formed on a top
surface of a dielectric substrate 10 made of polycarbonate or the
like, for example. The radiating element 6 passes through and is
supported by the dielectric substrate 10 in a direction of a
thickness of the dielectric substrate 10 while being electrically
insulated from the grounding conductor 11, and a radio signal is
fed from a radio apparatus (not shown) to the radiating: element 6.
While being electrically insulated from the grounding conductor 11,
the parasitic element 7 passes through and is supported by the
dielectric substrate 10 in the direction of the thickness of the
dielectric substrate 10. One end of the parasitic element 7 is
grounded in high frequency bands to the grounding conductor 11
through the varactor diode D and a through hole conductor 12 that
passes through and is filled into the dielectric substrate 10 in
the direction of the thickness of the dielectric substrate 10, and
the one end of the parasitic element 7 is also connected to a
terminal T through a resistor R. The terminal T is grounded in high
frequency bands to the grounding conductor 11 through a
high-frequency bypass capacitor C and a through hole conductor 13
that passes through and is filled into the dielectric substrate 10
in the direction of the thickness of the dielectric substrate
10.
A variable voltage direct-current power supply 30, whose voltage is
controlled by the controller 100 of the array antenna apparatus, is
connected to the terminal T. The controller 100 changes a backward
bias voltage Vb applied to the varactor diode D by the variable
voltage direct-current power supply 30, and this leads to change of
capacitance of the varactor diode D. Thus, the electric length of
the parasitic variable-reactance element A1 comprising the
parasitic element 7 is changed as compared to the electric length
of the feeding antenna element A0, and therefore, the a directivity
on horizontal plane of the array antenna apparatus can be changed.
Furthermore, the parasitic variable-reactance elements A2 to A6,
each of which comprises the other parasitic element 7, are
similarly constituted and thus have the similar function. The array
antenna apparatus configured as described above can be called an
electronically steerable passive array radiator antenna (ESPAR
antenna).
As described above, the first preferred embodiment of the present
invention shown in FIGS. 1 to 4 has a very simple structure as
compared to that of the array antenna apparatus of the prior art
shown in FIG. 12. For example, the use of the varactor diode D
makes it possible to realize the array antenna apparatus capable of
electronically controlling the directivity thereof using
direct-current voltages. The array antenna apparatus can be easily
mounted to electronic equipment such as a notebook type personal
computer or a PDA so as to serve as an antenna for a mobile
communication terminal, for instance. Moreover, even when the main
beam thereof is scanned in any direction on a horizontal plane, all
the parasitic variable-reactance elements A1 to A6 effectively
function as wave directors or reflectors and also greatly
facilitate the control of the directivity.
SECOND PREFERRED EMBODIMENT
FIG. 5 is a perspective view showing a configuration of an array
antenna apparatus according to a second preferred embodiment of the
present invention. The array antenna apparatus according to the
preferred embodiment comprises a dipole replacing a monopole of the
array antenna apparatus shown in FIG. 1.
Referring to FIG. 5, a feeding antenna element AA0 located in the
center of the array antenna apparatus is constituted by comprising
a pair of radiating elements 6a and 6b aligned with each other at a
predetermined distance therebetween, and one end of the radiating
element 6a and one end of the radiating element 6b, which face each
other, are connected to terminals T11 and T12, respectively. In
this case, the terminals T11 and T12 are connected to a radio
apparatus through a balanced transmission cable, and the radio
apparatus feeds a radio signal to the feeding antenna element
AA0.
Each of parasitic variable-reactance elements AA1 to AA6, which are
spaced at a predetermined angle on the circumference of a circle
around the feeding antenna element AA0, comprises a pair of
parasitic elements 7a and 7b arranged in line with each other at a
predetermined distance therebetween. One end of the parasitic
element 7a and one end of the parasitic element 7b facing each
other are connected to each other through a varactor diode D1, one
end of the varactor diode D1 is connected to a terminal T1 through
a resistor R1, and the other end of the varactor diode D1 is
connected to a terminal T2 through a resistor R2. A high-frequency
bypass capacitor C1 is connected between the terminals T1 and T2.
The variable voltage direct-current power supply 30 for applying a
backward bias voltage Vb to the varactor diode D1 is connected to
the terminals T1 and T2, in a manner similar to that of the first
preferred embodiment shown in FIG. 4.
The controller 100 changes the backward bias voltage Vb applied to
the varactor diode D1 of each of the parasitic variable-reactance
elements AA1 to AA6 through the terminals T1 and T2 by the variable
voltage direct-current power supply 30, and thus changes
capacitance of each varactor diode D1. Thus, the electric lengths
of the parasitic variable-reactance elements AA1 to AA6 each
comprising the parasitic elements 7a and 7b are changed as compared
to the electric length of the feeding antenna element AA0, and
therefore the a directivity on horizontal plane of the array
antenna apparatus can be changed.
As described above, the second preferred embodiment of the present
invention shown in FIG. 5 has a very simple structure as compared
to the array antenna apparatus of the prior art shown in FIG. 12.
For example, the use of the varactor diode D1 makes it possible to
realize the array antenna apparatus capable of electronically
controlling the directivity at a direct-current voltage. The array
antenna apparatus is easily mounted to electronic equipment such as
a notebook type personal computer or a PDA so as to serve as an
antenna for a mobile communication terminal, for instance.
Moreover, even when the main beam thereof is scanned in any
direction on a horizontal plane, all the parasitic
variable-reactance elements AA1 to AA6 effectively function as wave
directors or reflectors and also greatly facilitate the control of
the directivity.
MODIFIED PREFERRED EMBODIMENTS
In the above-mentioned preferred embodiments, the description is
given with regard to the array antenna apparatus for transmission.
However, the apparatus of the present invention can be used for
reception in a manner similar to that of the apparatus of the prior
art shown in FIG. 12, because the apparatus of the present
invention is a reversible circuit including no non-reversible
circuit. In the case of the array antenna apparatus for reception,
the radiating element 6 is an element for receiving and outputting
a radio signal, and the parasitic element 7 is an element that is
used for control of the directivity upon receipt of a radio signal
but does not output any radio signal. Therefore, in the case of the
array antenna apparatus for transmission and reception, the
radiating element 6 is an element which a radio signal is inputted
to and outputted from, and the parasitic element 7 is an element
which no radio signal is inputted to and outputted from.
In the above-described preferred embodiments, the six parasitic
variable-reactance elements A1 to A6 or AA1 to AA6 are used, but
the directivity of the array antenna apparatus can be
electronically controlled as long as the number of parasitic
variable-reactance elements is equal to at least one. The
directivity of a beam and a direction of a beam can be finely
controlled by increasing the number of parasitic variable-reactance
elements A1 to A4 or AA1 to AA4, and, for example, the beam width
of the main beam thereof can be also controlled so as to narrow the
beam width and thus sharpen the main beam.
Moreover, an arrangement of the parasitic variable-reactance
elements A1 to A6 or AA1 to AA6 is not limited to the
above-described preferred embodiments, and the parasitic
variable-reactance elements A1 to A6 or AA1 to AA6 can be arranged
at a predetermined distance from the feeding antenna element A0 or
AA0. That is, a distance d between the feeding antenna element A0
or AA0 and the parasitic variable-reactance elements A1 to A6 or
AA1 to AA6 does not necessarily have to be any constant.
Furthermore, the variable-reactance element 23 is not limited to
the varactor diodes D and D1, and it can be any element which can
control the reactance. Since each of the varactor diodes D and D1
is generally a capacitive circuit element, its reactance always
takes on a negative value. In an example of numeric values shown in
Table 1, zero or a positive value is used as impedance Z. The
reactance of the above-mentioned variable-reactance element 23 may
take on any value within a range from a positive value to a
negative value. For A this purpose, for example, the reactance can
be changed over a range from a positive value to a negative value
by inserting a fixed inductor in series with the varactor diode D
or D1, or by further increasing the length of the parasitic element
7.
EXAMPLES
The inventor performed the following simulation in order to check
performance of the array antenna apparatus according to the
above-described preferred embodiments. An analytical model shown in
FIGS. 6 and 7 is used in the simulation. Important parameters for
design of the array antenna apparatus according to the preferred
embodiments are as follows.
(1) The number N and lengths l.sub.n (n=1, 2, . . . , N) of
parasitic variable-reactance elements AA1 to AA6: Although N is
equal to 6 in the preferred embodiments, this is just an example.
Moreover, all the parasitic variable-reactance elements AA1 to AA6
are, preferably, of the same length l.sub.n in consideration of
360-degree scanning.
(2) The distance d between the feeding antenna element AA0 and the
parasitic variable-reactance elements AA1 to AA6.
(3) The reactance X.sub.n to be loaded or connected into the
parasitic variable-reactance element AAn.
Among these parameters, the above-mentioned parameters (1) and (2)
are unchangeable or non-adjustable parameters once they are
determined by designing, whereas the above-mentioned parameter (3)
is a parameter that can be electronically controlled within some
range by the varactor diode D1 as described above. In order to
obtain basic data for determining optimum parameters, various kinds
of characteristics were calculated by using the method of moments
when the parameters of the ESPAR antenna apparatus of the preferred
embodiments were changed to some extent. Analysis was performed,
assuming that the grounding conductor 11 was infinite and a dipole
antenna was arranged in free space. The analytical model is shown
in FIGS. 6 and 7. When sets of parameters take on values shown in
Table 1, Table 2 shows calculated values of input impedance Zin,
gain Gain, angles Deg (E.sub.max) and Deg (E.sub.min) when the
intensity of the electric field becomes a maximum value (E.sub.max)
and a minimum value (E.sub.min), respectively, and a ratio
E.sub.min /E.sub.max of the minimum value of the electric field, to
the maximum value thereof. In Table 1, Z.sub.n =X.sub.n.
TABLE 1 Sets of parameters used for analysis in cases Z.sub.n Case
N 1.sub.o 1.sub.n d Z.sub.1 Z.sub.2 Z.sub.3 Z.sub.4 Z.sub.5 Z.sub.6
Case 6 .lambda./4 0.91.sub.o .lambda./4 -j20 j0 -j20 +j20 j0 +j20 1
.OMEGA. .OMEGA. .OMEGA. .OMEGA. .OMEGA. .OMEGA. Case 1.1.lambda./4
2 Case .lambda./4 j5 -j10 j5 -j20 j20 -j20 3 .OMEGA. .OMEGA.
.OMEGA. .OMEGA. .OMEGA. .OMEGA. Case 1.1.lambda./4 4
TABLE 1 Sets of parameters used for analysis in cases Z.sub.n Case
N 1.sub.o 1.sub.n d Z.sub.1 Z.sub.2 Z.sub.3 Z.sub.4 Z.sub.5 Z.sub.6
Case 6 .lambda./4 0.91.sub.o .lambda./4 -j20 j0 -j20 +j20 j0 +j20 1
.OMEGA. .OMEGA. .OMEGA. .OMEGA. .OMEGA. .OMEGA. Case 1.1.lambda./4
2 Case .lambda./4 j5 -j10 j5 -j20 j20 -j20 3 .OMEGA. .OMEGA.
.OMEGA. .OMEGA. .OMEGA. .OMEGA. Case 1.1.lambda./4 4
Results of calculation of patterns of far radiation electric field
on a horizontal plane (relative values) are shown in FIGS. 8 to 11.
It has been shown that the parasitic variable-reactance elements
AA1 to AA6 operate as wave directors or reflectors by appropriately
selecting reactance X.sub.n in accordance with the values of the
gain Gain shown in Table 2 and the shapes of the patterns of
directivity shown in FIGS. 8 to 11. Moreover, as is apparent from
comparison among FIG. 8, FIGS. 9 and 10 and FIG. 11, it is
understood that the shape of the radiation pattern greatly changes
only by slightly changing the value of the distance d.
POSSIBILITY OF INDUSTRIAL UTILIZATION
As described in detail above, an array antenna apparatus according
to the present invention comprises a radiating element for
transmitting and receiving a radio signal therethrough; at least
one parasitic element incapable of transmitting and receiving any
radio signal, where the parasitic element is arranged at a
predetermined distance from said radiating element; a
variable-reactance element connected to said parasitic element; and
said array antenna apparatus changes directivity of said array
antenna apparatus by changing a reactance of said
variable-reactance element. Accordingly, the array antenna
apparatus according to the present invention has a very simple
structure as compared to that of the array antenna apparatus of the
prior art shown in FIG. 12, and, for example, the use of the
variable-reactance element such as a varactor diode makes it
possible to realize the array antenna apparatus capable of
electronically controlling the directivity at a direct-current
voltage. The array antenna apparatus is easily mounted to
electronic equipment such as a notebook type personal computer or a
PDA so as to serve as an antenna for a mobile communication
terminal, for example. Moreover, even when the main beam is scanned
in any direction on a horizontal plane, all parasitic
variable-reactance elements effectively function as wave directors
or reflectors and also greatly facilitate the control of the
directivity.
* * * * *